Jet Engine > Casing & Coatings

The final and often over looked part of the engine is the casing and coatings.  The casing is an important component that contains the hot and stressful story that results in a jet engine creating thrust.  Although simplistically represented in the model below, there are many smaller parts that form the casing.  As the casing protects and contains the engine, many other components are also protected by coatings.  These coatings protect components but also play an important role in managing damage especially for the turbine.

 

The casing of an engine performs an important role in protecting it during flight and when on the ground.  Getting a jet engine approved requires a number of tests like the fan-blade-off test and bird strike test which simulate disaster conditions.  A casing must be able to cope with a broken fan blade which can have an energy equivalent to a family car travelling at 100km/hr.  Additionally, the fan casing forms the path which bypass air takes to later stages of the engine for cooling.

Not experiencing the extremes of temperatures or stress that happens inside the engine, the casing still needs to be impact resistant, corrosion resistant, and lightweight whilst protecting the engine.  Composites meet all these criteria, and so we see parts of the casing such as the nose cone, nose cone fairing, impact panel and acoustic liners, splitters, core fairings, unison rings, and fast track liners made from a range of composites.  Once composites become more established and cost effective, larger components like the containment case and even fan blades will use this new group of materials.

The casing also has an important role in the compressor and turbines as it supports the static and rotating parts.  The stators in the compressor are held in place and attached to the casing.  Between the casing and rotating parts such as the compressor rotors and turbines, bearings or rollers are used to keep these components aligned.  This causes a lot of wear on the casing from these fast moving parts.  To prevent damage to the casing abradable coatings are thermally sprayed on the inside of the casing.  These coatings minimise the damage from the rollers/bearings, allow for damage inspection, and also create a better seal stopping air from leaking throughout the system.

Thermal Barrier Coatings or TBCs are also an important part to the jet engine.  These coatings are usually found in the combustor and on the turbine blades.  By coating the blades in a ceramic you gain oxidation and corrosion resistance whilst insulating the blades  from the high temperatures.  It also is useful in detecting damage to components making long term operation of the engine safer.